It is well known that use of low gamma photographic developers result in certain advantages in aerial surveillance. Included among the advantages are simplification of camera design since the need for automatic exposure control is greatly reduced, reduction in overexposure errors, and compression of the density range of the negative to fit the density range of the positive image to be produced. From a practical standpoint, the choice between high or low contrast aerial photography is dependent upon the particular situation and the information desired. At high altitude, a high contrast (high gamma) developer is needed to detect small variations in luminance and to compensate for scattering and flare. At low and medium altitudes, the fundamental advantages of low contrast (low gamma) developers are increased resolution due to finer grain development and a wider exposure latitude. Since aerial reconnaissance is in many instances concerned with low and medium latitude photography, there is a real need for an improved low gamma developer.
The patent literature is replete with disclosures of formulations for use as photographic developers. Examples of such patents include U.S. Pat. Nos. 3,804,624 and 3,865,591. These patents are considered to be pertinent to the invention disclosed herein since they describe formulations containing Phenidone (1-phenyl-3-pyrazolidone) and hydroquinone, ingredients of the developer composition of this invention. However, according to U.S. Pat. No. 3,804,624, addition of Phenidone to silver halide emulsions was unsuccessful since the accelerator compound is very susceptible to oxidation. In U.S. Pat. No. 3,865,591, a developer formulation is disclosed that contains three developing agents, namely, 3-pyrazolidones (Phenidone), dihydroxybenzenes (hydroquinone), and enediols. In examples of the patent, formulations are disclosed in which the amount by weight of hydroquinone used is more than ten times the amount of Phenidone. Such a high weight ratio of hydroquinone to Phenidone is incapable of providing a low gamma photographic developer.
It is a principal object of this invention, therefore to provide an oxidatively stable, low gamma photographic developer.
Another object of the invention is to provide a low gamma photographic developer which is especially adapted for the rapid processing of aerial film.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.